In order to increase the packing density of high heat generating components such as light emitting diodes, the wiring boards on which these components are mounted are required to achieve high heat dissipation. In order to obtain a wiring board having good heat dissipation properties, Patent Document 1 proposes a method for producing a wiring board, the method including applying an insulating water-soluble clay to a metal sheet as the substrate, thereby forming a heat-dissipating ceramic layer.    Patent document 1: Japanese Patent Application Laid-Open No. 2002-329939